The disclosures of the following priority applications are herein incorporated by reference: Japanese Patent Application No. 2000-277805 filed Sep. 13, 2000 Japanese Patent Application No. 2000-370695 filed Dec. 5, 2000
1. Field of the Invention
The present invention relates to an apparatus employed to conduct a surface inspection on a test piece such as a wafer during the process of manufacturing IC chips, liquid crystal display panels and the like.
2. Description of Related Art
Many different circuit patterns are stacked over a plurality of layers at a surface of a substrate such as a wafer to manufacture an IC chip or a liquid crystal display element panel. These circuit patterns are formed by stacking them one layer at a time on the wafer through a photolithography process or the like.
When manufacturing an IC chip, for instance, a resist is applied in a thin layer onto an oxide film formed at a surface of a wafer (substrate) and then the resist layer is exposed with a circuit pattern at a reticle by an exposure apparatus. Next, the resist having been exposed is removed through development processing, thereby forming a pattern constituted of a resist layer achieving an identical form (or a similar reduced form) to the circuit pattern at the reticle. Subsequently, after removing the exposed oxide film through etching, the remaining resist layer is removed to form a circuit pattern constituted of the oxide film layer at the surface of the wafer. An element such as a diode is formed through doping processing or the like implemented on the circuit pattern constituted of the oxide film layer. While there is a degree of variance with regard to the manufacturing method depending upon the type of IC being manufactured, the process of forming a specific circuit pattern layer as described above is normally performed repeatedly to stack a plurality of circuit patterns over many layers on the wafer.
When circuit patterns are stacked over numerous layers on the wafer in this manner, a surface inspection is conducted to verify that no defect, abnormality or the like has occurred in the circuit pattern formed in each layer. This inspection may be implemented when, for instance, a circuit pattern constituted of the resist layer has been formed. If a surface defect, an abnormality or the like such as a deformation of the circuit pattern, inconsistency in the film thickness of the resist layer or a scar is detected during the inspection, reclaim processing is implemented for this circuit pattern layer. Namely, the resist is stripped and then a new resist layer is applied and exposed.
If a defect, an abnormality or the like occurs at any of the circuit patterns when manufacturing an IC chip or the like by stacking the circuit patterns over multiple layers on the wafer, the acceptability of the IC chip as a product is compromised. For this reason, it is crucial to conduct an inspection to detect such defects, abnormalities and the like, i.e., to conduct a wafer surface inspection.
The surface inspections proposed in the related art include an inspection in which various types of inspection illuminating light are irradiated on the test piece (wafer) surface from different angles and the light reflecting at the test piece is directly observed visually by the inspector as the test piece is rotated or tilted.
Such an inspection method is generally referred to as a macro inspection. When a macro inspection is implemented through visual observation by the inspector, there is a risk of inconsistency manifesting in the inspection results due to varying judgment criteria, skills and the like among individual inspectors. In addition, the onus placed on the inspector is significant. Accordingly, the possibility of automating macro inspections has been examined and various automatic macro inspection apparatuses have been proposed. For instance, there is an apparatus that performs an automatic surface inspection by irradiating inspection illuminating light onto a surface of a test piece, receiving the diffracted light from a repetitive pattern formed at the surface of the test piece with an image-capturing device to take in a diffracted image and performing image-processing on the diffracted image.
However, in the surface inspection apparatus in the related art, the optimal settings cannot be automatically selected for the apparatus conditions (the illuminating light incident angle, the tilt angle of the test piece substrate, the wavelength of the illuminating light, the position at which the light exiting the test piece and entering the image-capturing device is received and the like) when capturing a diffracted image based upon the diffracted light from the circuit pattern (repetitive pattern) on the surface of the test piece. The optimal settings in this context refer to conditions under which the direction along which the diffracted light originating from the repetitive pattern advances roughly matches the direction along which the optical axis of the light-receiving optical system that receives the diffracted light extends and, in other words, they are conditions under which a diffracted image that is good enough to enable a surface inspection is obtained.
The optimal settings for the apparatus conditions change in correspondence to the pitch of the repetitive pattern formed on the test piece. Thus, the apparatus conditions must be adjusted in correspondence to the pitch of the repetitive pattern. However, in reality, the inspectors are often not informed of the design value set for the repetitive pattern pitch. Accordingly, in the surface inspection apparatus in the related art, the diffracted image of the test piece is displayed on the monitor and the inspector selects the optimal settings for the apparatus conditions by checking the diffracted image on the monitor. However, this method poses a problem in that it is not always easy for the inspector to accurately judge the optimal apparatus conditions and thus, the inspector must have significant skills and experience.
An object of the present invention is to provide a surface inspection apparatus capable of determining the optimal apparatus conditions under which a defect inspection is to be performed and thus conducting a highly reliable surface inspection even when the pitch of a pattern at the surface of a test piece is not known.
The surface inspection apparatus according to the present invention comprises an illuminating device that illuminates a test piece having a plurality of repetitive patterns with different pitches formed at a surface thereof, an image-capturing device that captures an object image based upon diffracted light originating from the test piece, a condition control device that sets or changes an apparatus condition under which the object image is captured with the image-capturing device and a condition determining device that takes in images of object images, each captured by the image-capturing device every time the apparatus condition is changed by the condition control device and determines an optimal setting for the apparatus conditions for inspecting the patterns based upon the images thus taken in. The condition determining device takes in images of object images based upon diffracted light fluxes from the individual repetitive patterns with different pitches and determines the optimal settings for the apparatus condition in correspondence to the individual repetitive patterns.
A plurality of optimal settings may be determined in correspondence to the plurality of repetitive patterns with different pitches. Alternatively, a single optimal setting may be determined based upon a specific parameter.
The surface inspection apparatus may further comprise a storage device that stores in memory an object image captured under the optimal settings determined by the condition determining device and a defect detection device that reads out the image stored in the storage device and detects a defect in a pattern formed at the test piece based upon the image thus read out.
The surface inspection apparatus may further comprise a storage device that stores in memory the optimal settings determined by the condition determining device so that when inspecting a test piece other than the test piece used to determine the optimal settings, the condition control device reads out the optimal settings from the storage device to set the apparatus conditions in conformance to the optimal settings thus read out.
The condition determining device may select as optimal settings the apparatus conditions under which an object image achieving a highest brightness value among a plurality of object images captured by varying the apparatus conditions has been captured, or it may perform quadratic differentiation on the change occurring in the highest brightness among the object images each obtained every time the apparatus conditions are changed to select the apparatus conditions under which a brightness peak value is achieved as optimal settings.
The apparatus conditions is constituted of at least one of; the angle of incidence of the illuminating light irradiated by the illuminating device onto the test piece, the angle at which the test piece is mounted, the wavelength of the illuminating light and the position at which the light exiting the test piece and entering the image-capturing device is received.
The plurality of repetitive patterns with varying pitches formed at the surface of the test piece are constituted of transfer patterns formed by exposing an original pattern with an exposure apparatus, with a plurality of transfer patterns exposed on the surface of the test piece under identical exposure conditions. This enables the surface inspection apparatus according to the present invention to capture object images based upon diffracted light fluxes originating from the individual repetitive patterns with respect to a pair of the transfer patterns formed at positions distanced from each other at the surface of the test piece with the image-capturing device, to determine the optimal settings for the individual repetitive patterns based upon the captured images with the condition determining device to compare the optimal settings corresponding to the pair of transfer patterns for each repetitive pattern and to select the optimal settings corresponding to one of the repetitive patterns.
Alternatively, the surface inspection apparatus may capture object images based upon diffracted light fluxes originating from the individual repetitive patterns with respect to a pair of the transfer patterns formed at positions close to each other at the surface of the test piece with the image-capturing device, determine the optimal settings for the individual repetitive patterns based upon the captured images with the condition determining device, compare the optimal settings corresponding to the pair of transfer patterns for each repetitive pattern and select the optimal settings corresponding to one of the repetitive patterns.
The image-capturing device is constituted of a two-dimensional image-capturing element having a plurality of pixels, and the condition determining device may set the brightness value corresponding to each pixel and the number of pixels as the specific parameter. In this case, the condition determining device may store in memory a plurality of tilt angles corresponding to the highest level of brightness achieved in the object images captured by the image-capturing device to select one tilt angle among the plurality of tilt angles based upon the specific parameter. Alternatively, the condition determining device may ascertain the number of pixels achieving brightness values equal to or higher than a predetermined brightness value and the average brightness values among the pixels at varying tilt angles to select the optimal tilt angle based upon the number of pixels and the average pixel brightness values thus ascertained.
The image-capturing device is constituted of a two-dimensional image-capturing element having a plurality of pixels, and the condition determining device may store in memory a plurality of tilt angles corresponding to the highest level of brightness in an object image captured by the image-capturing device to select a plurality of optimal settings by determining the order of priority among the plurality of tilt angles based upon the brightness values at the individual pixels and the number of pixels.